Radio Frequency (RF) transceivers typically use some form quadrature modulation to achieve higher spectral efficiency. The two most common transceiver architectures are the direct conversion and heterodyne conversion receivers. A direct conversion receiver requires the Radio Frequency Local Oscillator (RFLO) to generate two output signals, referred to as the in-phase and quadrature carriers, whose relative phases are ninety degrees apart. In applications using a heterodyne receiver, an Intermediate Frequency Local Oscillator (IFLO) generates two signals whose relative phases are ninety degrees apart. However, one limitation of the heterodyne receiver architecture is a need for a significant amount of attenuation at the xe2x80x9cimage frequencyxe2x80x9d in the front-end filter and the Low Noise Amplifier (LNA). The amount of attenuation of the xe2x80x9cimage frequencyxe2x80x9d is called the image rejection ratio of the filter.
A modification of the heterodyne architecture called the Weaver architecture is commonly used in an integrated receiver to achieve additional image rejection. This architecture requires both the local oscillator at radio frequencies as well as that at intermediate frequencies to generate two signals each whose relative phases are ninety degrees apart.
It would be advantageous to have a circuit that generates two, high spectral purity, local oscillator carriers with a relative phase shift of ninety degrees that may be used in the modulation and demodulation process. It would be of further advantage for the circuit to be area and cost efficient.